Backup energy storage module with voltage leveling

1. An energy storage module comprising: one or more capacitor banks, each including one or more capacitors, wherein the one or more capacitors includes a first capacitor and a second capacitor connected in series for storing energy, wherein a first terminal of the first capacitor is coupled to a first terminal of the second capacitor at a node, and a second terminal of the first capacitor is coupled to a circuit ground node, and a second terminal of the second capacitor is coupled to a regulated direct current (DC) voltage through a first resistor; a first voltage regulator coupled to the one or more capacitor banks and configured to, during a normal mode of operation, provide the regulated DC voltage to charge the one or more capacitors of each of the capacitor banks; wherein each of the one or more capacitor banks includes a voltage leveling circuit coupled to the one or more capacitors and configured to maintain a specific voltage on each of the one or more capacitors, wherein the voltage leveling circuit includes: a passive leveling portion having a first bleed resistor coupled between the node between the first and second capacitors and circuit ground, and a second bleed resistor coupled between the second terminal of the second capacitor and circuit ground; and an active leveling portion including: a second voltage regulator circuit coupled to the node between the first and second capacitors and configured to actively provide a first specific voltage to the node between the first and second capacitors; and a third capacitor coupled in parallel with a control resistor between circuit ground and a control input of the second voltage regulator; and an output circuit coupled to each of the one or more capacitor banks and configured to, during a backup mode of operation, provide an output voltage derived from an output of each of the one or more capacitor banks, wherein the output circuit includes a control unit configured to regulate and combine the output of each of the one or more capacitor banks.

2. The energy storage module as recited in claim 1 , wherein each of the one or more capacitors comprises supercapacitors including a double-layer dielectric.

3. The energy storage module as recited in claim 1 , wherein the second bleed resistor is configured to bleed off to circuit ground voltage that is in excess of a second specific voltage at the a second terminal of the second capacitor, and the first bleed resistor is configured to bleed off to circuit ground voltage that is in excess of the first specific voltage at the node between the first and second capacitors.

4. The energy storage module as recited in claim 1 , wherein a capacitance value of the third capacitor is selected to control a slew rate and corresponding overshoot of the second voltage regulator such that the second voltage regulator operates sufficiently to maintain the first specific voltage at the first capacitor.

5. The energy storage module as recited in claim 4 , wherein the capacitance value of the third capacitor is in a range of 300 microfarads (uf) to 400 uf.

6. The energy storage module as recited in claim 1 , wherein each of the one or more capacitor banks includes a discharge circuit coupled in parallel with the first resistor, wherein the discharge circuit is configured to provide a discharge path from the output of each of the one or more capacitor banks to circuit ground in response to a connector of the energy storage module being disconnected from a mating connector.

7. The energy storage module as recited in claim 6 , wherein the mating connector provides a path to circuit ground, and when the connector of the energy storage module is disconnected from the mating connector the circuit ground connection is broken, wherein the loss of circuit ground causes a transistor within the discharge circuit to conduct current from the output of each of the one or more capacitor banks to circuit ground.

8. The energy storage module as recited in claim 6 , wherein the discharge circuit is further configured to provide a discharge path from output of each of the one or more capacitor banks to circuit ground in response to receiving a discharge enable signal.

9. A storage subsystem comprising: a plurality of data storage modules, each including a non-volatile storage and a volatile storage; and one or more backup power units, each configured to provide backup power to the plurality of data storage modules in response to a power loss to the storage subsystem, wherein each backup power unit includes: one or more capacitor banks, each including one or more capacitors, wherein the one or more capacitors includes a first capacitor and a second capacitor connected in series for storing energy, wherein a first terminal of the first capacitor is coupled to a first terminal of the second capacitor at a node, and a second terminal of the first capacitor is coupled to a circuit ground node, and a second terminal of the second capacitor is coupled to a regulated direct current (DC) voltage through a first resistor; a first voltage regulator coupled to the one or more capacitor banks and configured to, during a normal mode of operation, provide the regulated DC voltage to charge the one or more capacitors of each of the capacitor banks; wherein each of the one or more capacitor banks includes a voltage leveling circuit coupled to the one or more capacitors and configured to maintain a specific voltage on each of the one or more capacitors, wherein the voltage leveling circuit includes: a passive leveling portion having a first bleed resistor coupled between the node between the first and second capacitors and circuit ground, and a second bleed resistor coupled between the second terminal of the second capacitor and circuit ground; and an active leveling portion including: a second voltage regulator circuit coupled to the node between the first and second capacitors and configured to actively provide a first specific voltage to the node between the first and second capacitors; and a third capacitor coupled in parallel with a control resistor between circuit ground and a control input of the second voltage regulator; and an output circuit coupled to each of the one or more capacitor banks and configured to, during a backup mode of operation, provide an output voltage derived from an output of each of the one or more capacitor banks, wherein the output circuit includes a control unit configured to regulate and combine the output of each of the one or more capacitor banks.

10. The storage subsystem as recited in claim 9 , further comprising a management unit coupled to the one or more backup power units and to the plurality of data storage modules and configured to monitor and manage system information including environmental and system status information, wherein in response to a loss of power to the storage subsystem, the management unit is configured to provide a backup signal indicating that a loss of power has occurred, and in response to the backup signal, the one or more backup power units is configured to provide the backup power to each of the plurality of data storage modules, and each of the plurality of data storage modules is configured to write unwritten data stored within the volatile storage to the non-volatile storage.

11. The storage subsystem as recited in claim 9 , wherein each of the one or more capacitors comprises supercapacitors including a double-layer dielectric.

12. The storage subsystem as recited in claim 9 , wherein the second bleed resistor is configured to bleed off to circuit ground voltage that is in excess of a second specific voltage at the a second terminal of the second capacitor, and the first bleed resistor is configured to bleed off to circuit ground voltage that is in excess of the first specific voltage at the node between the first and second capacitors.

13. The storage subsystem as recited in claim 9 , wherein a capacitance value of the third capacitor is selected to control a slew rate and corresponding overshoot of the second voltage regulator such that the second voltage regulator sufficiently operates to maintain the first specific voltage at the first capacitor.

14. The storage subsystem as recited in claim 13 , wherein the capacitance value of the third capacitor is in a range of 300 microfarads (uf) to 400 uf.

15. The storage subsystem as recited in claim 9 , wherein each of the one or more capacitor banks includes a discharge circuit coupled in parallel with the first resistor, wherein the discharge circuit is configured to provide a discharge path from the output of each of the one or more capacitor banks to circuit ground in response to either of a connector of the energy storage module being disconnected from a mating connector or in response to receiving a discharge enable signal.

16. A system comprising: an electronic device; a primary power supply configured to provide power to the electronic device during a normal operational mode; and a backup power unit configured to provide backup power to the electronic device in response to power loss to the system, wherein the backup power unit includes: one or more capacitor banks, each including one or more capacitors, wherein the one or more capacitors includes a first capacitor and a second capacitor connected in series for storing energy, wherein a first terminal of the first capacitor is coupled to a first terminal of the second capacitor at a node, and a second terminal of the first capacitor is coupled to a circuit ground node, and a second terminal of the second capacitor is coupled to a regulated direct current (DC) voltage through a first resistor; a first voltage regulator coupled to the one or more capacitor banks and configured to, during a normal mode of operation, provide the regulated DC voltage to charge the one or more capacitors of each of the capacitor banks; wherein each of the one or more capacitor banks includes a voltage leveling circuit coupled to the one or more capacitors and configured to maintain a specific voltage on each of the one or more capacitors, wherein the voltage leveling circuit includes: a passive leveling portion having a first bleed resistor coupled between the node between the first and second capacitors and circuit ground, and a second bleed resistor coupled between the second terminal of the second capacitor and circuit ground; and an active leveling portion including: a second voltage regulator circuit coupled to the node between the first and second capacitors and configured to actively provide a first specific voltage to the node between the first and second capacitors; and a third capacitor coupled in parallel with a control resistor between circuit ground and a control input of the second voltage regulator; and an output circuit coupled to each of the one or more capacitor banks and configured to, during a backup mode of operation, provide an output voltage derived from an output of each of the one or more capacitor banks, wherein the output circuit includes a control unit configured to regulate and combine the output of each of the one or more capacitor banks.